In particular, the method according to the invention makes use of a technique for localized electrochemical reduction so as to form, on the surface of a piece, hydrophilic areas surrounded by hydrophobic areas.
The pieces made of composite material comprising such localized hydrophilic areas are intended to be used in particular for producing spots capable of chemical recognition, such as biochips (also called DNA chips), or in the field of microfluidics, which relates to flows in structures involving characteristic sizes of the order of a micrometer, in order to obtain fluid or particle transport areas (biological cells).
In fact, for such applications, it is necessary for the hydrophilic part of the substrate, or active part, to be localized, and for the rest of the substrate to be chemically and physically inert, so as not to influence the reactions taking place in the active part.
For the applications under consideration, the use of substrates made of polymer material has recently developed. In fact, these substrates offer, compared with the silicon or the glass conventionally used, many advantages such as ready formulation, a low cost and good biocompatibility.
A process for the fabrication of microstructures having geometrically diverse configurations, in a piece comprising superimposed layers of various polymers, is known, for example, from document U.S. Pat. No. 6,221,227. However, this process comprises a large number of steps, which makes its implementation complex.
The local modification of substrates made of polytetrafluoroethylene, or PTFE (generally sold under the trademark Teflon®) by electrochemical reduction is, moreover, known. Reference may be made to the following publications: C. Combellas et al., Polymer 44 (2003) 19-24; C. Combellas et al., Polymer 45 (2004) 4669-4675; C. Combellas et al., J. Phys. Chem. B (2004), 108, 6391-6397.
The use of the electrochemical process makes it possible to readily adjust the sizes of the hydrophilic areas through the selection of the electrode used, allows easy large-scale transposition, and is also inexpensive. Moreover, PTFE provides the advantage of good thermal resistance and a low cost.
However, this polymer has drawbacks that are extremely detrimental for the applications under consideration. In fact, it has a poor surface finish, in particular a rough character which cannot be improved, even by polishing. In addition, it exhibits creep from 60° C. onward, and is opaque.